ROT13 Cipher

Shifts every letter in your text 13 positions through the alphabet, wrapping from Z back to A, while leaving digits, spaces, and punctuation untouched — a simple Caesar cipher with a fixed shift of half the 26-letter alphabet.

Type or paste text into the input box; the ROT13 result appears automatically below it. There's a single box rather than separate encode/decode buttons, since ROT13 works the same way in both directions.

Applying ROT13 to `Hello, World!` produces `Uryyb, Jbeyq!`. Pasting that result back into the tool returns `Hello, World!` again — running the cipher twice always cancels itself out.

Shifting a 26-letter alphabet by 13 twice equals shifting by 26, which is the same as not shifting at all, since 26 is exactly the alphabet's length — that's the mathematical reason ROT13 needs no separate decode mode.

ROT13 is a long-standing convention on forums and newsgroups for hiding spoilers, puzzle solutions, or punchlines from casual view — a reader has to make a deliberate choice to decode the text rather than being confronted with it immediately.

Because the shift amount is fixed and public knowledge, ROT13 provides no real confidentiality: anyone who recognizes the pattern can decode it by eye, and it should never be used to protect passwords, personal data, or anything genuinely sensitive.

The transformation runs entirely in your browser via client-side JavaScript; the text you type is never uploaded to a server or stored.